Dump truck hoist mechanism



June 8, 1943. aD. R MERCHANT 2,321,406

DUMP TRUCK HOIST MECHANISM Filed Feb. 5, 1942 5 Sheets-Sheet 1 Dom 2. Mczwmr June 8, 1943. 4 D. R. MERCHANT 2,321,406

DUMP TRUCK HOIST MECHANISM DnNLo IZ. Melzcmwr June 8, 1943. D. R. MERCHANT .DUMP TRUCK HoIsT MECHANISM Filed Feb. 5, 1942 3 Sheets-Sheet 3 Damm Z. Mezoaam' Patented June 8, 1943 DUMP TRUCK HOIST MECHANISM Donald R. Merchant, Minneapolis, Minn., assigner to St. Paul Hydraulic Hoist Company, Minneapolis, Minn., a corporation of Michigan Application February 5, 1942, Serial No. 429,620

'7 Claims.

This invention relates to improvements in hoist mechanisms for dump trucks.

The usual hoist mechanism for lifting and swinging a dump body about its hinge connection with the chassis frame of the truck comprises a hydraulic cylinder arranged lengthwise and forwardly of the body hinge and pivotally connected at a forward end to the chassis frame. A piston rod extending rearwardly from the cylinder is then connected by a crosshead pin to the body at a point above the level of the body hinge so that, when the piston rod is projected rearwardly by admission of fluid under pressure to the cylinder, the pushing forces or thrust will be exerted along a line above the body hinge to tilt and raise the body with respect to the chassis. The fluid for thus actuating the piston rod is taken from a pump driven through a power takeoff device from the truck engine.

Such structures, and all variations thereof with which I am familiar, have one great disadvantage. This lies in the fact that, particularly as the lifting action first starts, the cylinder and piston rod are Working at a mechanical disadvantage since the force is exerted along a line only slightly above the body hinge and the leverage is accordingly small. As a result the fluid pressure reaches a maximum at once and a great shock load is placed on the fluid pump and its bearings, the power takeoff and drive line and even on the transmission of the truck engine itself, thus causing excessive wear and frequent breakdowns of some parts.

In some hoist structures lifting arms or links are arranged between the piston rod and dump body in the attempt to secure a mechanical advantage and reduce the fluid pressure but these structures also will reach a maximum pressure almost immediately thus introducing shock effects to the driving elements, almost, if not entirely, as bad as the direct lift types.

With the foregoing facts in mind it is the primary object of my invention to provide a hoist mechanism in which a gradual acceleration of the fluid pressure will be attained and in which a novel and effective lifting means is employed in order to secure a mechanical advantage particularly during the initial lifting operations to thus not only eliminate shock effects but also reduce the maximum fluid pressure finally attained in the system.

Another object is to provide a hoist mechanism of this nature embodying both the principles of the lever and the wedge or cam in its mechanical movements and functioning to secure-the maximum possible advantagefrom each. lStill another object is to provide such a'hoist-mechanism in a simple and durable form and' capable of a wide variety of variations and applications as may be required in different installations.

These and other more detailed and specific objects will be disclosed inv the course of thefollowing specication, reference being had to the accompanying drawings, in which- Fig. l is a longitudinal Vertical sectional view, through the body and chassis-suframes, of a dump truck equipped with my invention, the body frame being shown in full lines as partially raised and in brokenv lines in its fully raised position.

Fig. 2 is an enlarged perspective View of the cam or wedge device or track used in my hoist mechanism.

Fig. 3 is a fragmentary plan view ofthe structure of Fig. l, the body subframe and other parts being shown in the position they occupy when the body is lowered.

Fig. 4 is a similarA View but showing-a modified hoist mechanism embodying apair ofv cylinders and associated parts.

Fig. 5 is an enlarged fragmentary longitudinal and vertical section'through the chassis andbody subframes and showing a further modification of the hoist mechanism.

Fig. 6 is a fragmentary plan View of the struc-- vture of Fig. 5.

Fig. 7 is an enlarged vertical cross sectional View taken substantially along the line l-"l in Fig. 3.

Referring now more particularly and by reference characters to the drawings there is shown in Fig. 1 thereof portions of a chassis A andthe body B of a dump truck to which parts'the'hoist mechanism of my invention is applied. In such application a chassis frame or sub-frame lil and body frame or subframe I'I are generally secured `atop the chassis and beneath ,the ibody, respectively, although as a matter of course the hoist might be made a part of the .chassis .and body themselves if so desired.

The body frame il I nea-r its rear end carries depending hinge plates or side brackets l2 which are pivoted upon hinge pins i3 carried at the rear of the chassis frame lil, said pins eXtending transversely and forming a hinge axis about which the body may be tilted or raised upwardly at its forward end withrespect to the truck'chasof dumping the contents of the body B through its rear end.

The frame I is rectangular to nt upon the chassis A and comprises side members I4, a forward cross member I and a rear cross member I6 all secured rigidly together and mounted in any suitable manner upon the chassis. The body frame IIis valso generally rectangular t0 fit beneath the body B and comprises longitudinal underirame members or channels I1`across and atop which are mounted the cross members I8 joined along their ends by side members I9. The longitudinal members I1 of the frame II come to rest along the side members I4 of the frame I0 (Fig. 7) in the lowered or normal transporting position of the body B and thus a space is formed between these members to accommodate the hoist mechanism without interfering with lowering movements of the body.

The hoist mechanism, as shown in Figs. l, 2, 3 and 7 particularly, comprises -aV cylinder 2li arranged lengthwise between the frame members I4-I1 forwardly of the body hinge axis and secured at its forward end to a cross member 2I, arranged upon transversely extending pivot pins 22 which pivot in the side members I4 so that the cylinder may swing upwardly and downwardly at its rear end. A valve 23 is supported on the member 2| and controls the admission of fluid into, or exhaust of the iluid from, the forward portion of the cylinder, such fluid flowing through a line connection device 24 from a power takeoff driven pump (not shown) in usual manner. The valve 23 is operated by a link 25 and crank 26 from the usual control lever in the truck cab (also not shown). A piston rod or plunger 21 extends from the rear end of the cylinder 23 and carries a cross-head pin 2B at its rear end which usually is connected to the body frame II either directly or through lifting arms pivoted between the frames I and II. Neither connection is here shown but it is understood that such arrangements provide that a rearward thrust by the piston rod will exert angular forces on the body above its hinge axis at pins I3 in order to swing the body upward at its forward end'.

In accordance with my invention, however, the rear end of the piston rod 21 has a bifurcated head member or fork 29 which carries the crosshead pin 28 and between the sides of this fork there is mounted a flanged roller 35 which is journaled upon the pin. The crosshead pin then carries a link member consisting of a pair of links 3| pivoted upon end portions of the lpin and at their other ends pivoted upon a connecting pin 32 which is transversely extended and supported by short angle members 33 welded, or otherwise secured, in lengthwise, parallel and transversely spaced positions between two adjacent cross members I8 of the body frame I I. The links thus form lever extensions of the piston rod and connect the same to the body.

`A cam or wedge device designated generally at 34 is arranged lengthwise on frame I0 in the path of the rearward movement of the piston rod 21 and comprises an inclined cam way or track or wedge surface 35 extending rearwardly (or toward the body pivot) and upwardly from its forward nose or end upon which the roller 30 will Y rest in the normal, lowered position of the body and in the retracted position of the piston rod. The extreme forward end of the track 35 is substantially horizontally extended in the form of a rest or nose surface as designated at 36 and meets the more sharply inclined portion of the track through a curved section 31, the function of which will presently appear. The track extends upwardly to a point well above the level of the body hinge axis on the pins I3 and to a point rearwardly of the position occupied by the connecting pin 32 in the lowered position of the body.

The cam or wedge device is forwardly supported by an angular bracket member 38 upon a cross bar 39 secured between the sides of the frame Ii) and is supported at the rear end by a foot portion 4) which rests upon thek rear cross member IB of the frame, these parts being welded or bolted to the frame members IIE and 39 to rigidly mount the device. The foot portion 43 is formed at the rear of a downwardly angled leg v4I extending from the track or cam way and an upright web 42 stiffens all parts in usual manner. Other webs or brace fins 43 are extended from the bracket member 38 to adjacent parts of the track forfurther stiening the structure. The width of the rest member 38 is greater than that of the cam way 35 for laterally stabilizing the mounting.

It will be noted that the cam device is supported not only against downward displacement but is especially well braced against rearward movement by the factthat the lbracket member 38 and foot 43 are braced rearwardly against upright parts of the frame members 39 and I6.

Stops or stop pads 44 are secured to the angle members 33 which support the connecting pin 32 and are disposed in the path of rearward movements of the links 3| as will presently appear, these pads being angularly disposed and braced by brace wings 45.

In the normal or starting position of the parts the roller 3i) rests upon the horizontally extending rest surface 36 of the cam way or track 35 and the links 3I extend angularly upwardly and rearwardly from the crosshead pin 28 to the connecting pin 32. This condition is illustrated in Fig. 5 although there the crosshead and plunger arrangement is somewhat different and yet to be described. Y

In operation now, asiluid` is admitted to the cylinder 20 to project the piston rod 21 rearwardly, the roller 3B is caused to travel upwardly and rearwardly along the track 35, being guided therealong by the longitudinal alignment of cylinder and cam device. 'I'he result of the angularity of this track surface or cam way 35 is to translate the rearward thrust of the piston rod, through a wedge-like or camming action, to a more nearly upward thrust or lifting force upon the links 3|, which links of course transmit this force to the body frame II and raise the body. As the roller moves upwardly along the camway or track in this operation the links 3l gradually swing towardy and iinally beyond, erect positions, with respect to the axis of the crosshead pin 28, but the force exerted through the links issubstantially in an upward direction until the roller reaches the upper extremity or summit of the cam way, whereupon the links, having swung past the dead center or upright position, contact the stop pads 44, which are properly located to engage thelinks at this time. 'The pads or stops 44, of course act then to limitl further rearward folding or buckling of the links with respect tothe pin 32 thus forming a rigid connection between the piston rod and the bodyV and, as the piston rod now continues to moverearwardly, its thrust is exerted directly upon the/body to complete the hoisting operation.

Y In the return or lowering movement of the body the piston rod moves forwardly or into the cylinder and the roller 30 uponreaching the cam Way or track 35 travels downwardly along thesame until it nally comes to rest upon the rest surface 3B.

It will be apparent from the foregoing that, as the lifting operation beginsthe mechanical advantage of the wedging or camming action ofthe track 35 upon the plungerrend, and resulting upward lift upon the links, is employed at the time when such advantage is needed greatly. In other words, it is at such time, when lifting the -body through the first few degrees, that the piston rod is moving in its most nearly horizontal direction and the lleverage exerted about the body hinge axis is least in the usual hoist construction. Then in my structure as the roller 30-reaches the top of the cam way the links become rigid with respect to body and piston rod and the lift is directly exerted upon the body but, at -this time, the cylinder has tilted well upwardly on the axis of the pins 22 and the thrust of the piston rod acts at a considerable advantage and leverage about the axis of the hinge pins I3. Thus my invention acts to provide an initial increase in effective lifting forces when the leverage capable of being exerted by the piston rod by direct connection to the body is least and then shifts the connection directly to the body when the piston rod has been elevated to a point at which it has an effective leverage advantage on the body.

As the roller 36 approaches the foot of the inclined cam way r track 35 it is guided gradually upward by the radius at the curved surface 3l and thus the full load of the body lifting action is brought to bear upon the cylinder in a gradual manner. This is important in that the fluid pressure may accelerate gradually thus eliminating shock effects not only on the piston rod and cylinder but upon the driving pump, power takeoff, truck engine transmission and all connecting parts. This elimination of the shock load greatly reduces wear and breakage. In addition, due to the fact that the lift operates at all times with a mechanical advantage, as compared to other types of hoists, the maximum pressure reached by the iiuid is also reducedand this fact too is important.

At the time that the roller 39 leaves the cam way 35 there may possibly be a momentary increase in pressure but this is largely counteracted by the fact that, at such time, the body is already at a dumping angle and a part of its load has fallen clear, thus reducing the overall load on the hoist. rIhis will be clearly evident in Fig. 1 wherein the body A is shown at a dumping angle although the roller has not yet left the cam way and the hoist is still operating under the advantage of the upward wedging or camming lift action.

As shown in Fig. 4 the hoist mechanism may include a parallel arrangement of two lift cylinders, 2li-20a, two rollers Sli-38a, and two cam devices 3dr-34a arranged in transverse spacing.

in and between the frames lil and Il where increased lifting forces are required. In such construction there are of course two pairs of the links 3l, two pins 32 and two sets of supporting members 33 for the pins as clearly shown. 'Ihe construction and operation of individual units are the same as previously described. The cylinders may be controlled by a single valve but the same isnotshown iny this view since ythe connections are obvious.

As shown in Figs. 5 and 6 each cylinder 20 may actuate two rollers 46-41 similar to lthe v4previously described rollers 39- arranged at thelends of a pin lt8supporteolbya widelyextended crosshead 49 secured to the end of the*pistonirody 21. Each roller then operates-'upon separate camv devices 34-35@ which-are mounted and constructed as previously described, and -separatefpairs of links Eli- El-make connections tti-pins S24-32a arranged Asubstantially as shown in- Fig'. 4.- The camdevices 34-34a are-spacedapart at opposite sides of the axis of thecylinder 20 and the effect is to give added lateral stabilityandy greater' distribution of working forces. Corresponding partsexcept as above-noted are given the-'same reference numerals as in the other-figures ofv the drawings.

. Another obvious modification-of the structure is to employ two complete units of thepluralltype shown in Figs. 5 and'6 in aparallel arrangement as shown in Fig. 4, wherein two cylinders, four rollers and four cam devices wouldbe used.

-It is understood that my hoist mechanism may be employedv as well in side dumping trucks in which case the cylinder and cam device would be arranged in transverse planes instead of longitudinally as herein shown and described. -The piston rod would then -of coursev move toward the body hinge in therequiredmanner.

It isv understood that suitable modifications may be made in the structure as disclosed, provided such modifications comewithin the spirit and scope of the appended claims.

Having now therefore fully illustrated and described my invention, what I claim to be new and desireto protect by LettersPatent is:

1-. VIn a dump truck hoist for swinging a truck body upwardly about its pivot connectionwitli the truck frame, comprising a-hoist mechanism having a plunger connected to the body and adapted to exert thrust forces in a direction tending toward the pivot connection of the body, a link member connected at its endsr between the plunger and body, cam means on the frame having a cam surface operative for guiding said plunger upwardly as it initially moves toward said pivot connection and transmitting said thrust forces through the link member upwardly to the body, and means for rendering the -link member and plunger rigid with respect to each other to transmit said thrust forces directly to the body when the plunger clears the said cam means.

2. In a hoist mechanism for a dump truck body for swinging said body upwardly about the axis of its hinge connection with the truck, a plunger arranged for movement in an endwise direction toward said hinge axis and for upward and downward movements, a cam device having an inclined surface for engaging the plunger and moving the same upward as it travels toward said hinge axis, links pivotally connected at lower ends to the plunger and at upper ends to the body for transmitting lifting forces to the body at angles with respect to the plunger axis as said plunger moves upwardly, said links being adapted to swing about their upper end connections from forwardly and downwardly angled positions rearwardly to substantially vertical depending positions with respect to said upper end connections as the plunger is guided upwardly by said cam surface, and stop means for engaging the links as they swing to such upright positions and rendering the links rigid with respect to both plunger and body for transmitting thrust forces from the plunger directly to the body along a line coincident with the plunger axis.

3. In a hoist mechanism for a dump truck body for swinging said body upwardly about the axis of its hinge connection with the truck, a plunger arranged for movement in an endwise direction toward said hinge axis and for upward and downward movements, a cam device on the truck having an inclined surface for engaging the plunger and moving the same upward as it travels toward said hinge axis. links pivotally connected at lower ends to the plunger and at upper ends to the body for transmitting lifting forces to the body at angles with respect to the plunger axis as said plunger moves upwardly, said links being adapted to swing about their upper end connections from forwardly and downwardly angled positions rearwardly to vertically depending positions with respect to said upper end connections as the plunger is guided upwardly by said cam surfaces, and stop means carried by the body for rearwardly engaging the links as they swing to said depending positions and preventing further swinging movements thereof, said links then transmitting thrust forces from the plunger directly to the body along a line coincident with the axis of the plunger.

4. In a hoist mechanism for raising a dump truck body about its hinge axis, a lifting cylinder, a piston rod therein and movable toward the hinge axis of the body, connecting means between the piston rod and body, a cam device rigidly supported in the path of the piston rod and having an inclined surface adapted to guide they piston rod upwardly as it moves towardthe hinge axis and thereby exert upward lifting forces on the body through said connecting means, said inclined surfaces of the cam device having a rest portion at its lower end to support the piston rod in the lowered position of the body and said rest portion meeting the said inclined surface through a gradually curving portion to thereby guide the piston rod upwardly to the steeper remainder of said surface.

5. A hoist mechanism for tilting a dump truck body about its hinge axis on the truck frame, comprising a plunger movable in a rearward direction toward the hinge axis of the body and swingable in an upright plane with respect to the truck frame, a cam device rigidly supported on the truck frame and having a rearwardly and upwardly inclined track surface located in the path of the rear end of the plunger for camming the plunger upwardly as it is moved rearwardly, a link member pivoted at the lower end to the rear end of the plunger and extending normally in an upwardly and rearwardly inclined direction therefrom, and the upper end of the link member being pivoted to the body to exert upward and rearward pushing forces thereon in response to rearward movement of the plunger.

6. A hoist mechanism for tilting a dump truck body about its hinge axis on the truck frame, comprising a plunger movable in a rearward direction toward the hinge axis of the body and swingable in an upright plane with respect to the truck frame, a roller on the rear end of the plunger, a cam device rigidly supported from the truck frame and having kan upwardly and rearwardly inclined trackway located in the path of the roller for urging the rear end of the plunger upwardly as it moves rearwardly, a link pivotally connected at the lower end to the plunger on the axis of the roller and extending Y in a generally upward and rearward direction the truck frame, a cam device rigidly supported on the truck frame and having a rearwardly and upwardly inclined track surface located in the path of the rear end of the plunger for camming the plunger upwardly as it is moved rearwardly, a link member pivoted at the lower end to the rear end of the plunger and extending normally in an upwardly and rearwardly inclined direction therefrom, and the upper end of the link member being pivoted to the body to exert upward and rearward pushing forces thereon in response to rearward movement of the plunger, the said cam device having a rearwardly declining leg portion extending from its rear end and braced against a part of the truck frame.

DONALD R. MERCHANT. 

